1. Field of the Invention
The present invention relates to seals for sealing the space between a floating roof and an inner tank wall within a storage tank for petrochemical or other liquid products.
2. History of the Prior Art
It is standard practice in the field of large storage tanks such as oil storage tanks having floating roofs to provide the floating roof with one or more seals. Such seals act to seal the space between the outer rim of the floating roof and the inner tank wall while at the same time allowing the floating roof to rise or drop as the height of the liquid product within the storage tank varies. Such seals are necessary in order to prevent harmful hydrocarbon vapors from escaping through the space between the floating roof and the inner tank wall and entering the atmosphere. For some applications, a single seal is installed on the floating roof so as to seal the space between the roof and inner tank wall. For other applications, a primary seal provides the main sealing function while a secondary seal disposed above the primary seal traps any vapors that may escape through the primary seal.
Seals for floating roofs within storage tanks can assume a variety of different configurations. Examples of the different possible configurations of floating roof seals are provided by U.S. Pat. No. 4,308,968 of Thiltgen et al., U.S. Pat. No. 5,078,293 of Lippiello, U.S. Pat. No. 5,103,992 of Lippiello et al. and U.S. Pat. No. 5,301,828 of McKay. Such patents are commonly assigned with the present application. The seals depicted by these patents assume various configurations, and typically utilize vapor barrier fabrics in conjunction with other materials. Several of the configurations utilize shoe seals which are suspended from the outer edge of the floating roof for disposition adjacent and biasing against the inner tank wall. A further example of a floating roof seal is provided by copending application Ser. No. 09/082,028 of Richard P. King et al., "Seal For Floating Roof Of Storage Tank", which application is commonly assigned with the present application.
The floating roof seals described in the above-mentioned patents and application are capable of sealing the space between the floating roof and the inner tank wall effectively. However, there is a continuing need for floating roof seals that provide other options and alternatives in terms of design, fabrication and installation. Seals of relatively simple design and low cost may present particular advantages for many installations.
In the case of secondary seals mounted above primary seals for the floating roof, it would be desirable to provide such a seal of limited height so as to extend only a relatively small distance above the floating roof. This would provide the tank with increased storage capacity by increasing the maximum height to which the floating roof can rise. Such seals should be of relatively simple construction, and the light in weight. At the same time, such seals should be made of highly durable materials so as to require a minimum of maintenance and to provide a long service life. The seals must be water tight so as to keep rain water out of the liquid product within the tank. Where a vapor barrier fabric forms a part of the seals, the fabric should be disposed for ease of inspection and replacement when necessary, and should be oriented so as to shed rainwater which might otherwise collect thereon.